docs: def get_linenumbertable(self):
          """
          a sequence of (code_offset, line_number) pairs.
  
          reference: http://docs.oracle.com/javase/specs/jvms/se7/html/jvms-4.html#jvms-4.7.12
          """  # noqa
  
          lnt = self._lnt
          if lnt is None:
              buff = self.get_attribute("LineNumberTable")
              if buff is None:
                  lnt = tuple()
              else:
                  with unpack(buff) as up:
                      lnt = tuple(up.unpack_struct_array(_HH))
              self._lnt = lnt
          return lnt